It is common practice to provide a gas turbine engine with two separate manifolds for the supply of fuel to the combustion apparatus of the engine. One manifold is for the main supply of fuel to the combustion apparatus and the other is for the supply of fuel for the purpose of engine starting. Thus when the engine is started, fuel is supplied to the combustion apparatus through both manifolds until combustion is initiated. Fuel supply through the main manifold is maintained to sustain engine operation, whereupon the fuel flow to the starter manifold is reduced to a very low flow rate.
During normal engine operation, it is normal practice to allow small amounts of fuel to continue to flow through the starter manifold and into the engine combustion apparatus in order provide cooling of the starter manifold. However this can result in an undesirable increase in the smoke produced by the engine. If the fuel flow is stopped, the starter fuel jets supplied with fuel by the starter manifold can become blocked with carbon and localized "hot-spots" can occur within the combustion apparatus.
It is an object of the present invention to provide a gas turbine engine fuel system in which fuel flow through the starter manifold is eliminated during normal engine operation with the substantial elimination of such carbon blockage and localized "hot spots".
According to the present invention, a gas turbine engine fuel system comprises a source of pressurized fuel, main and starter fuel manifolds interconnected with and adapted to receive fuel from a source of pressurized fuel, means interconnecting each of said manifolds with the interior of the combustion apparatus of a gas turbine engine and adapted to direct fuel into said combustion apparatus interior, and valve means adapted to optionally interrupt the fuel supply to said starter fuel manifold, means being provided to interconnect said starter fuel manifold with a drains system which is arranged to be at a pressure lower than that operationally within said combustion chamber, whereby when, during engine operation, said fuel flow to said starter manifold is interrupted by said valve means, pressurized gases originating from within said combustion equipment flow through and thereby purge said starter manifold and said means interconnecting said starter manifold and said combustion apparatus, and exhaust into said drains system through said means interconnecting said starter manifold and said drains system, flow limiting means being provided in said means interconnecting said starter manifold and said drains system to at least limit the amount of fuel flowing into said drains system when said fuel supply to said starter manifold is not interrupted by said valve means.